CONJUGATION IN BLEPHARISMA UNDULANS 671 



gether with experiments on the effects of chemicals of differ- 

 ent kinds, will be published in another place. In the present 

 paper I desire only to present the observations on division and 

 paedogamous conjugation. 



Division of Blepharisma undulans 



When conditions are fairly uniform in the cultures Blephar- 

 isma divides about once in twenty-four hours. No regular 

 rate, however, is characteristic; at one period during the earlier 

 stages of the culture the organisms divided as often as three 

 times in one day, but later the division rate fell as low as two 

 divisions in ten days. 



When ready to divide, the cells appear slightly swollen in 

 the middle and a new peristome appears in the posterior half of 

 the cell (fig. 4) . The individuals become sluggish and, even before 

 the adoral membranelles are visible, a contractile vacuole ap- 

 pears immediately posterior to the mouth and in the most 

 swollen portion. The membranelles of the posterior adoral 

 zone first appear as cilia slightly more conspicuous than the 

 cilia on the general surface. At this time there is no trace of 

 the posterior peristome. A shallow furrow soon appears, how- 

 ever, and this gradually deepens, while the membranelles grow 

 in size and vibrate with a rhythmic motion from anterior to pos- 

 terior (fig. 5) . The division furrow begins immediately posterior 

 to the central vacuoles, below the point of maximum swelling, 

 and then cuts in from the ventral surface towards the dorsal. 

 Throughout this period I have been unable to see the conspicu- 

 ous undulating membrane on either half of the dividing organ- 

 ism. On the posterior cell it does not appear until the mouth 

 breaks through in the last five minutes of division. In the 

 anterior half I have watched its vibrations up to the time of the 

 beginning of constriction, when it could not be seen again until 

 the end stages. Whether this anterior membrane is thrown 

 off and another formed to replace it I cannot say. Possibly 

 the mouth being closed at this period of division, the mem- 

 brane is folded down on the floor of the peristome and is thus 



